ADULT HIP DYSPLASIA (DDH)
Developmental Acetabular Deficiency | Progressive Arthritis | Joint-Preserving vs Arthroplasty
CROWE CLASSIFICATION
Critical Must-Knows
- Lateral CEA less than 25° = acetabular dysplasia (Wiberg angle)
- Periacetabular osteotomy (PAO) = gold standard joint preservation in young adults
- True acetabulum must be identified in Crowe III-IV for component placement
- Femoral shortening required in Crowe II-IV to avoid nerve stretch injury
- High hip center increases revision risk - restore anatomy when possible
Examiner's Pearls
- "DDH is the leading cause of hip arthritis in young women
- "Tönnis angle greater than 10° indicates lateral acetabular deficiency
- "Hartofilakidis classification focuses on acetabular development (preferred by some)
- "Shelf procedures augment lateral coverage but do not reorient acetabulum
Clinical Imaging
Imaging Gallery
Critical Adult DDH Exam Points
Acetabular Anatomy
Lateral center edge angle (CEA) under 25° is diagnostic. Normal is 25-40°. CEA measures lateral coverage of femoral head on AP radiograph. Tönnis angle greater than 10° indicates abnormal acetabular slope.
Crowe Classification
Based on femoral head migration. Type I = subluxation under 50%. Type II = 50-75%. Type III = 75-100%. Type IV = complete dislocation. Higher grades need femoral shortening to avoid sciatic nerve palsy.
PAO vs THA Decision
PAO for young patients under 40 with minimal arthritis (Tönnis grade 0-1). THA for older patients or established arthritis (Tönnis grade 2-3). Joint space must be preserved for PAO success.
THA Technical Challenges
Restore anatomy to true acetabulum. High hip center increases dislocation and wear. Femoral anteversion often increased (monitor during reaming). Sciatic nerve at risk with limb lengthening over 4cm.
Quick Decision Guide
| Patient Scenario | Crowe Grade | Treatment | Key Pearl |
|---|---|---|---|
| Age under 40, painful hip, preserved joint space | I (under 50% subluxation) | Periacetabular osteotomy (PAO) | Reorients acetabulum - best long-term preservation |
| Age under 40, early arthritis, CEA under 20° | I-II (50-75% subluxation) | Consider PAO if Tönnis grade under 2 | Success depends on remaining cartilage quality |
| Age over 50, established arthritis | I-II (under 75% subluxation) | THA - standard technique with small modifications | Restore center of rotation, avoid high hip center |
| Any age, severe dysplasia with dislocation | III-IV (over 75% subluxation) | THA with subtrochanteric shortening osteotomy | Lengthen under 4cm to protect sciatic nerve |
CASTRadiographic Assessment of Hip Dysplasia
Memory Hook:CAST your assessment on plain films - these 4 measurements determine treatment!
HALFCrowe Classification of DDH
Memory Hook:HALF way measures the hip's journey out of the socket - 50%, 75%, 100%!
CARTILAGEPAO Contraindications
Memory Hook:Protect the CARTILAGE - if it's gone, PAO fails and THA is inevitable!
Overview and Epidemiology
Adult hip dysplasia represents persistent acetabular underdevelopment from infancy or childhood, leading to progressive hip instability and premature osteoarthritis. The condition is often undiagnosed in infancy and presents in early adulthood when symptomatic.
Why Adult DDH Matters
DDH is the leading cause of hip arthritis in women under 40. Early recognition allows joint-preserving surgery (PAO) before irreversible cartilage damage. Missed diagnosis leads to THA in the third or fourth decade.
Demographics
- Female predominance: 9:1 ratio due to hormonal laxity
- Age at presentation: 20-40 years (painful subluxation)
- Bilateral: 20-30% have contralateral involvement
- Ethnic variation: Higher in First Nations, Southern Europeans
Clinical Impact
- 10% of total hip arthritis from DDH in young adults
- Progression: 50-75% develop arthritis by age 50 if untreated
- Quality of life: Significant functional limitation in third decade
- Economic: Early THA with high revision burden
Anatomy and Pathophysiology
The Biomechanical Cascade of DDH
Shallow acetabulum → increased contact stress → rim overload → labral tears → progressive cartilage loss → early arthritis. The lateral CEA measures this coverage - under 25° doubles contact stress on remaining cartilage.
Normal vs Dysplastic Acetabulum
| Feature | Normal Hip | Dysplastic Hip | Consequence |
|---|---|---|---|
| Lateral CEA | 25-40° | Under 25° | Increased joint reactive force |
| Tönnis angle | 0-10° | Greater than 10° | Lateral instability and migration |
| Acetabular anteversion | 15-20° | Often greater than 25° | Anterior instability, labral damage |
| Contact area | 500-600 mm² | Under 300 mm² | Doubled or tripled contact stress |
Associated Soft Tissue Pathology
Labral Pathology
- Anterosuperior labral tears: 90% of symptomatic DDH
- Hypertrophy from chronic edge loading
- Ossification in long-standing cases
- Intrasubstance degeneration
Capsular Changes
- Capsular laxity: Contributes to instability
- Redundancy in chronic subluxation
- Adhesions in false acetabulum (Crowe IV)
- Hypertrophic ligamentum teres
Classification Systems
Crowe Classification (Most Common)
Based on degree of femoral head migration superiorly, measured on AP pelvis radiograph.
| Grade | Femoral Head Position | Acetabular Development | Treatment Implications |
|---|---|---|---|
| I | Under 50% superior migration, mostly in socket | Shallow but identifiable acetabulum | Standard THA or PAO possible |
| II | 50-75% migration, at level of acetabular rim | Moderate deficiency, true acetabulum visible | THA requires shortening or high hip center |
| III | 75-100% migration, above acetabulum | Severely deficient, false acetabulum forming | Subtrochanteric osteotomy for anatomic placement |
| IV | Complete dislocation, no contact with true socket | Rudimentary acetabulum, well-developed false socket | Complex reconstruction with bone grafting |
Crowe Measurement Technique
Measure the distance from the inter-teardrop line to the center of the femoral head. Divide by the height of the pelvis (teardrop to iliac crest). Result under 10% = I, 10-15% = II, 15-20% = III, over 20% = IV.
Clinical Assessment
History
- Groin pain: Anterolateral or anterior, worse with activity
- Clicking or catching: Labral pathology common
- Instability: Sensation of subluxation or giving way
- Childhood history: Hip screening, bracing, or surgery
- Family history: DDH in relatives (genetic component)
- Age at onset: Typically 20-40 years when symptomatic
Examination
- Gait: Trendelenburg gait (abductor insufficiency)
- Leg length: Apparent shortening in high dislocation
- ROM: Usually preserved early, decreases with arthritis
- Impingement: Anterior pain with flexion-adduction-IR
- Apprehension: Clunk with flexion-abduction-ER (instability)
- Abductor strength: Often weak (lever arm dysfunction)
Beware Bilateral DDH
Contralateral hip is dysplastic in 20-30% of cases. Always obtain full pelvis radiographs, not just symptomatic side. Bilateral PAO may be staged 6-12 months apart.
Special Clinical Tests
Physical Examination Sequence
Watch for Trendelenburg gait - trunk shifts over stance leg due to abductor weakness. Positive Trendelenburg test (pelvis drops on opposite side) in 40-60% of symptomatic DDH.
Apparent vs true shortening. In high dislocation, apparent shortening from pelvic tilt. Measure from ASIS to medial malleolus (true) and umbilicus to malleolus (apparent).
Assess flexion (normally 120°+), abduction (45°), adduction (30°), and rotation. Loss of internal rotation often first sign of arthritis. Document for PAO vs THA decision.
FADIR test (flexion-adduction-internal rotation) for anterosuperior labral tear. FABER test (flexion-abduction-external rotation) for posterior impingement or SI joint.
Investigations
Imaging Protocol
AP pelvis - weight-bearing, coccyx centered over pubic symphysis. Measure lateral CEA, Tönnis angle, assess arthritis grade. False profile view measures anterior CEA.
Key measurements:
- Lateral CEA under 25° = dysplasia
- Tönnis angle greater than 10° = lateral deficiency
- Anterior CEA under 20° = anterior deficiency
3D CT pelvis for surgical planning (PAO or THA). Assesses acetabular version, bony defects, location of true acetabulum in Crowe III-IV. Allows templating and virtual correction.
Gold standard for labral pathology. Sensitivity over 90% for labral tears. Assesses cartilage quality (Outerbridge grading). Helps determine PAO candidacy or need for arthroscopy.
In equivocal PAO candidates, arthroscopy can directly visualize cartilage. Outerbridge grade 3-4 changes = poor PAO candidate. Can address labral tears at time of PAO (staged or simultaneous).
Radiographic Measurements
| Measurement | Normal Range | Dysplasia Threshold | Clinical Significance |
|---|---|---|---|
| Lateral CEA (Wiberg) | 25-40° | Under 25° | Primary diagnostic criterion for lateral dysplasia |
| Tönnis Angle | 0-10° | Greater than 10° | Measures acetabular slope - predicts progression |
| Anterior CEA (false profile) | Greater than 20° | Under 20° | Anterior deficiency requires specific PAO correction |
| Acetabular Index (Sharp angle) | Under 40° | Greater than 43° | Alternative measure of lateral deficiency |
Management Algorithm
Initial Conservative Approach
Indications: Asymptomatic or mild symptoms, CEA 20-25° (borderline), older patients declining surgery.
Conservative Treatment Steps
Avoid high-impact activities (running, jumping). Low-impact exercise (swimming, cycling) maintains fitness without excessive loading. Weight management critical.
Strengthen hip abductors (gluteus medius) to compensate for biomechanical disadvantage. Core stability and pelvis control. Stretching hip flexors and IT band.
NSAIDs for symptom control (avoid chronic use). Paracetamol for baseline pain. Intra-articular steroid injection can provide temporary relief and confirm intra-articular source.
Annual radiographs to monitor progression. If joint space narrows or symptoms worsen despite therapy, surgical consultation indicated.
When Conservative Fails
Progression to surgery is indicated when: (1) pain limits function despite therapy, (2) radiographic progression (joint space loss), or (3) patient desire for definitive treatment before irreversible damage.
Surgical Technique
Bernese Periacetabular Osteotomy - Step by Step
Positioning: Supine on radiolucent table with affected hip at table edge. C-arm access for AP and lateral views.
PAO Surgical Steps
Incision from ASIS along iliac crest. Dissect interval between sartorius (femoral nerve) and tensor fascia lata (superior gluteal nerve). Subperiosteal elevation of iliacus off inner table.
Through same incision, curved osteotome directed posteriorly and inferiorly to cut ischium 10mm medial to acetabular rim. This cut exits just medial to acetabulum posteriorly.
Straight osteotome directed medially along superior pubic ramus. Exit 10mm medial to acetabular rim anteriorly. Protect obturator neurovascular bundle with retractor.
From AIIS superiorly toward SI joint (10-15cm). Incomplete posteriorly to maintain posterior column continuity. Use curved osteotome. Monitor with fluoroscopy.
Complete ischial cut with Gigli saw passed from intrapelvic to extrapelvic. Mobilize fragment with Schanz pins. Rotate laterally and anteriorly to increase coverage.
Fix with 3-4 cortical screws from ilium into mobilized fragment. Confirm hip congruity and improved CEA (target 30-35°) on fluoroscopy. Avoid overcorrection (pincer).
Intraoperative Assessment
Final lateral CEA should be 30-35° - adequate correction without overcorrection. Tönnis angle should be 0 to negative 5°. Confirm hip remains congruent through full ROM.
Complications
| Complication | Incidence | Risk Factors | Management |
|---|---|---|---|
| Sciatic nerve palsy (THA) | 1-5% (up to 10% in Crowe IV) | Lengthening over 4cm, inadequate shortening | Usually neurapraxia - observation, PT, may recover 6-18 months |
| Lateral femoral cutaneous nerve injury (PAO) | 10-15% | Smith-Petersen approach, excessive retraction | Usually temporary dysesthesia, resolves 3-6 months |
| PAO nonunion | 2-5% | Smoking, inadequate fixation, bone quality | ORIF with bone graft and plate if symptomatic |
| Intra-articular fracture (PAO) | 1-5% | Osteotomy extends into joint | Convert to THA if severe; ORIF if minimal displacement |
| THA dislocation | 5-10% (higher in DDH) | High hip center, component malposition, laxity | Closed reduction, brace, revision if recurrent |
| Aseptic loosening (THA) | 15-25% at 15 years | High hip center, inadequate bone stock, young age | Revision THA with bone grafting |
| Heterotopic ossification | 10-20% | Extensive dissection, male gender | Prophylaxis with indomethacin or radiation |
Recognizing Sciatic Nerve Injury Early
Immediate postoperative foot drop or numbness after THA in high dislocation = sciatic palsy. Document exam pre-closure. If noted immediately, consider shortening revision urgently (within 24-48 hours) to decompress nerve.
Postoperative Care and Rehabilitation
PAO Recovery Timeline
Touch weight-bearing with crutches. DVT prophylaxis (enoxaparin or rivaroxaban). Pain control with multimodal analgesia. Early mobilization to prevent stiffness.
Touch to 25% weight-bearing. Gentle hip ROM exercises. No active hip flexion against gravity (protects iliopsoas). Continue crutches. Monitor for signs of nonunion.
Increase to full weight-bearing if radiographs show healing. Formal physical therapy for abductor strengthening. Progress to single crutch then cane. Return to activities of daily living.
Full weight-bearing without aids. Progress to impact activities. Return to work (desk job 6-8 weeks, manual 3-4 months). High-impact sports delayed to 12 months.
Annual radiographs for 5 years to monitor for arthritis progression. Low-impact exercise encouraged. Watch for loss of ROM or recurrent pain (suggests progression).
PAO Recovery Reality
PAO recovery is long - expect 3-4 months to full function. Patients should be counseled preoperatively. Peak improvement is 12-18 months. Some never regain pre-DDH athletic ability.
Outcomes and Prognosis
PAO Outcomes
| Outcome Measure | Success Rate | Key Determinants |
|---|---|---|
| Conversion to THA avoided at 10 years | 85-90% | Preop Tönnis grade 0-1, adequate correction, age under 40 |
| Patient satisfaction | 80-85% | Realistic expectations, good cartilage quality, minimal complications |
| Return to sports | 60-70% | Low-impact sports better outcomes than high-impact |
Predictors of PAO Failure
Tönnis grade 2 or higher at time of surgery predicts failure. Joint space under 2mm, patient age over 40, and inadequate correction (final CEA under 25°) also predict poor outcomes.
THA Outcomes in DDH
Favorable Factors
- Crowe I-II classification
- Anatomic cup placement
- Adequate bone stock
- Modern implants (highly cross-linked polyethylene)
- Proper leg length restoration
Unfavorable Factors
- Crowe III-IV classification
- High hip center
- Young patient age (under 50)
- Poor bone quality
- Femoral shortening osteotomy (adds complexity)
Key Studies: 20-year registry data shows THA in DDH has higher revision rates than primary OA - 15-25% vs 5-10% in OA. Younger age at surgery and severe dysplasia are main risk factors.
Evidence Base and Key Trials
PAO Outcomes in Young Adults with Hip Dysplasia
- Mean follow-up 10 years after PAO in 140 hips
- Survivorship free from THA: 89% at 10 years, 74% at 20 years
- Best outcomes in patients under 35 with Tönnis grade 0-1
- Complications occurred in 13%, mostly nerve injuries (temporary)
THA in Developmental Dysplasia of the Hip: Registry Analysis
- Cumulative revision rate for DDH THA: 15.2% at 15 years vs 7.8% for OA
- Crowe III-IV hips have 2.5x higher revision risk than Crowe I
- High hip center placement increases revision risk by 40%
- Uncemented acetabular components perform better than cemented in DDH
Femoral Shortening in THA for High Hip Dislocation
- Sciatic nerve palsy rate: 1.4% with shortening vs 5.7% without
- Osteotomy union rate 95% at 6 months
- Functional outcomes equivalent to standard THA at 2 years
- Allows anatomic cup placement in Crowe III-IV hips
High Hip Center in THA for Dysplasia: Biomechanical Study
- High hip center (over 35mm superior to teardrop) increases hip reactive force by 30-40%
- Loosening rate 18% vs 6% for anatomic placement at 10 years
- Polyethylene wear accelerated in high hip centers
- Even 10mm superior placement increases force significantly
Arthroscopy at Time of PAO for Labral Pathology
- Combined arthroscopy and PAO in 60 hips with labral tears
- 95% had anterosuperior labral pathology requiring debridement or repair
- Outcomes equivalent to PAO alone at 2-year follow-up
- Adds 30-45 minutes to operative time
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Young Woman with Hip Pain and Dysplasia
"A 32-year-old woman presents with 2 years of progressive left groin pain. Pain is worse with activity and relieved by rest. She has no history of childhood hip problems. Examination shows full ROM but positive FADIR test. AP pelvis radiograph demonstrates lateral CEA of 18°, Tönnis angle of 15°, and Tönnis grade 1 arthritis. What is your assessment and management?"
Scenario 2: THA Planning in Crowe III Dysplasia
"A 58-year-old woman requires THA for severe arthritis secondary to DDH. Preoperative radiographs show Crowe type III dysplasia with the femoral head 5cm superior to the true acetabulum. She has a well-developed false acetabulum. Walk me through your surgical planning and technique."
Scenario 3: Postoperative Nerve Palsy After THA
"You have just completed a THA for Crowe type II dysplasia in a 52-year-old woman. Intraoperative lengthening was approximately 3.5cm. In recovery, she has a complete foot drop and numbness over the dorsum of the foot. How do you manage this?"
MCQ Practice Points
Anatomy Question
Q: What is the normal range for the lateral center edge angle (Wiberg angle) and what value indicates dysplasia? A: Normal lateral CEA is 25-40°. A value under 25° indicates acetabular dysplasia. The CEA is measured on AP pelvis radiograph as the angle between a vertical line through the femoral head center and a line from the center to the lateral acetabular edge. It quantifies lateral coverage of the femoral head.
Classification Question
Q: Describe the Crowe classification of developmental hip dysplasia. A: Crowe classification grades DDH based on degree of femoral head superior migration: Type I = subluxation under 50% (head mostly in socket), Type II = 50-75% subluxation (head at rim level), Type III = 75-100% subluxation (head above socket), Type IV = complete dislocation with false acetabulum. Higher grades require femoral shortening to avoid nerve injury during THA.
Treatment Question
Q: What are the key indications and contraindications for periacetabular osteotomy (PAO)? A: Indications: Symptomatic acetabular dysplasia (CEA under 25°), age under 40-45 years, minimal arthritis (Tönnis grade 0-1), preserved joint space (over 2mm). Contraindications: Advanced arthritis (Tönnis grade 2-3), inadequate cartilage (Outerbridge 3-4), reduced joint space (under 2mm), age over 45, large osteophytes. PAO success depends on remaining cartilage quality.
Complications Question
Q: What is the safe limit for limb lengthening during THA in dysplastic hips, and what is the risk of exceeding it? A: The safe limit for acute limb lengthening is generally under 4cm. Lengthening beyond this threshold significantly increases the risk of sciatic nerve palsy due to nerve stretch. In Crowe III-IV hips with greater than 4-5cm superior migration, femoral shortening osteotomy should be performed to allow anatomic cup placement without excessive lengthening. Sciatic nerve palsy incidence rises from 1-2% to 5-10% when lengthening exceeds 4cm.
Outcomes Question
Q: How do THA outcomes in developmental dysplasia compare to primary osteoarthritis? A: THA in DDH has higher revision rates than primary OA. Registry data shows 15-year revision rates of 15-25% for DDH vs 5-10% for OA. Poor prognostic factors include Crowe III-IV classification, young patient age (under 50), high hip center placement, and inadequate bone stock. Modern techniques emphasizing anatomic cup placement and femoral shortening when needed have improved outcomes.
Australian Context Question
Q: What does the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) report about THA in DDH? A: The AOANJRR Annual Report 2023 shows cumulative revision rate for DDH THA is 15.2% at 15 years vs 7.8% for osteoarthritis. Crowe III-IV hips have 2.5 times higher revision risk than Crowe I. High hip center placement increases revision risk by 40%. Uncemented acetabular components outperform cemented in DDH. This data emphasizes the importance of anatomic reconstruction and appropriate patient selection.
Australian Context and Medicolegal Considerations
AOANJRR Data on DDH
- Higher revision burden: 15.2% at 15 years vs 7.8% for OA THA
- Crowe grade matters: Type III-IV have 2.5x higher revision rate
- High hip center: 40% increased revision risk with superior placement
- Uncemented cups: Better long-term outcomes than cemented in DDH
- Young age: Patients under 55 have higher revision rates
Australian Guidelines
- ACSQHC Hip and Knee Arthroplasty Clinical Care Standard: Emphasizes informed consent about higher revision risk in DDH
- Recommend anatomic cup placement when feasible
- DVT prophylaxis: Extended prophylaxis (28-35 days) for PAO
- Registry participation: Mandatory reporting to AOANJRR
Medicolegal Considerations in DDH Surgery
Key documentation requirements:
- Preoperative counseling: Document discussion of higher revision risk (15-25% vs 5-10% in OA), nerve injury risk (1-5% in high dislocation), longer recovery for PAO (3-4 months)
- Surgical planning: CT imaging and templating should be documented for complex cases
- Informed consent: Specific risks including nerve palsy, dislocation, revision surgery
- Postoperative monitoring: Document neurological examination immediately after THA
- Common litigation issues: Failure to warn about higher revision risk, inadequate preoperative planning leading to high hip center, nerve injury without documented informed consent
Australian Hospital Systems
Public Hospital Pathway
- DDH assessment in public orthopaedic clinics
- Long waitlists for elective PAO or THA (6-12+ months)
- PAO typically performed at tertiary centers with expertise
- Medicare covers surgical costs
- Limited access to 3D CT planning in some centers
Private Hospital Pathway
- Faster access (weeks to months)
- Private health insurance covers prosthesis (partial)
- Out-of-pocket costs for gaps (surgeon, hospital)
- Better access to advanced imaging and planning software
- May need prior approval for complex implants
Adult Hip Dysplasia
High-Yield Exam Summary
Key Measurements
- •Lateral CEA under 25° = dysplasia (normal 25-40°)
- •Tönnis angle greater than 10° = abnormal slope
- •Anterior CEA under 20° = anterior deficiency
- •Joint space under 2mm = poor PAO candidate
Crowe Classification
- •Type I = under 50% subluxation (in socket) - standard THA or PAO
- •Type II = 50-75% subluxation (at rim) - THA with shortening or high center
- •Type III = 75-100% subluxation (above socket) - subtrochanteric osteotomy
- •Type IV = complete dislocation - complex THA with femoral shortening
Treatment Algorithm
- •Age under 40 + Tönnis 0-1 + CEA under 25° = PAO
- •Age over 45 or Tönnis 2-3 = THA
- •Crowe I-II = standard THA to true acetabulum
- •Crowe III-IV = THA with femoral shortening (under 4cm lengthening)
- •PAO success = 85-90% at 10 years if well selected
Surgical Pearls
- •PAO: reorient acetabulum to CEA 30-35° (avoid overcorrection)
- •THA: restore anatomy to true acetabulum, avoid high hip center
- •Femoral shortening when lengthening would exceed 4cm
- •Neuromonitoring for Crowe III-IV THA
- •Long stem to bridge subtrochanteric osteotomy
Complications
- •Sciatic nerve palsy: 1-5% (up to 10% in Crowe IV)
- •LFCN injury in PAO: 10-15% (usually temporary)
- •PAO nonunion: 2-5%
- •THA dislocation: 5-10% (higher than primary OA)
- •Revision rate: 15-25% at 15 years (vs 7-8% in OA)